Antibacterial activity and mode of action of acetone crude leaf extracts of under-investigated Syzygium and Eugenia (Myrtaceae) species on multidrug resistant porcine diarrhoeagenic Escherichia coli

Abstract

Background Diarrhoea, a global economically important disease burden affecting swine and, especially piglets, is commonly caused by infection with entero-toxigenic E. coli (ETEC). Adherence of ETEC to porcine intestinal epithelial cells following infection, is necessary for its pathogenesis. While antimicrobials are commonly given as therapy or as feed additives for prophylaxis against microbial infections, the concern over increased levels of antimicrobial resistance necessitate the search for safe and effective alternatives in livestock feed. Attention is shifting to natural products including plants as suitable alternatives to antimicrobials. The activity of acetone crude leaf extracts of nine under-explored South African endemic plants from the Myrtaceae family with good antimicrobial activity were tested against pathogenic E. coli of porcine origin using a microplate serial dilution method. Bioautography, also with p-iodonitrotetrazolium violet as growth indicator was used to view the number of bioactive compounds in each extract. In vitro toxicity of extracts was determined against Caco-2 cells using the 3-(4,5-dimethythiazolyl-2)-2,5-diphenyltetrazolium bromide reduction assay. The antimicrobial susceptibility of E. coli isolates was tested on a panel of antimicrobials using the Kirby-Bauer agar diffusion method while the anti-adherence mechanism was evaluated using a Caco-2 cell enterocyte anti-adhesion model. Results The MIC of the extracts ranged from 0.07–0.14 mg/mL with S. legatii having the best mean MIC (0.05 mg/mL). Bioautography revealed at least two active bands in each plant extract. The 50% lethal concentration (LC 50 ) values ranged between 0.03–0.66 mg/mL. Eugenia zeyheri least cytotoxic (LC 50 = 0.66 mg/ml) while E. natalitia had the highest cytotoxicity (LC 50 = 0.03 mg/mL). All the bacteria were completely resistant to doxycycline and colistin sulphate and many of the plant extracts significantly reduced adhesion of E. coli to Caco-2 cells. Conclusions The extracts of the plants had good antibacterial activity as well as a protective role on intestinal epithelial cells against enterotoxigenic E. coli bacterial adhesion. This supports the potential use of these species in limiting infection causes by E. coli . Some of these plants or extracts may be useful as phytogenic feed additives but it has to be investigated by animal feed trials.

Evaluation of in-vivo antidiarrhoeal and in-vitro antibacterial activities of the root extract of Brucea antidysenterica J. F. Mill (Simaroubaceae)

“…The MIC and MBC results from this experiment showed that the root extract of B. antidysenterica has the ability to inhibit and kill bacteria. The MIC of an extract is regarded as good if the values are less than 0.1 mg/mL, moderate if it is between 0.1 and 0.625 mg/mL and weak when it is above 0.625 mg/mL [40,57]. Based on this, the MIC of 80% hydro-methanolic crude extract of B. antidysenterica was ranged from moderate to weak against the tested bacteria strains.…”

The ultrastructural damage caused by Eugenia zeyheri and Syzygium legatii acetone leaf extracts on pathogenic Escherichia coli

“…In a recent study, acetone leaf crude extracts of Eugenia zeyheri and Syzygium legatii had excellent antimicrobial activity with MICs varying from 0.04 to 0.23 mg/ml on clinical and reference strains of E. coli. It also reduced the attachment of E. coli to intestinal cells in a Caco-2 cell adhesion assay [15].…”

Phytochemical Screening, Mathematical Analysis and Antimicrobial Activity of Methanolic Seed Extract of Hunteria Umbellata

“…The susceptibility of organisms to different antibiotics were tested using the disk diffusion method as described [21,23]. On freshly prepared Mueller Hinton agar and standardized by the method of Famuyide et al [24] and National Committee for Clinical Laboratory Standard (NCCLS) [22] using some selected antibiotics namely: tetracycline (30µg), pefloxacin (10µg), ampiclox (30µg), streptomycin (30µg), gentamicin (10µg), erythromycin (10µg), ciprofloxacin (10µg), amoxicillin (30µg), penicillin G (10µg), septrin (30µg) metronidazole (20 μg/disk) and imipenem (10 μg/disk). For each combination of the antibiotics and the bacterial strains, the experiment was performed in triplicate.…”